Hmm... it looks like mail... mmmh, it tastes like mail... it _is_ mail!
Once upon a time (Tuesday, April 29, 1997 to be precise), Robert Horne wrote 

letter to All about "External Programs"...
 RH> Hi all! Can somebody tell me how to execute external programs, such as
 RH> EXE or COM files in assembler?
Sure! This should do the trick:
======
; start your program by minimizing your programs memory usage
         mov       bx,sp
         add       bx,15
         shr       bx,4                          ; stack size in para's
         mov       ax,ss
         add       bx,ax                         ; bx points to end of stack
         mov       ax,es                         ; es points to psp at
         sub       bx,ax                         ; beginning of program
         mov       ah,4ah                        ; resize memory block
         int       21h
         jc        error                         ; unlikely, but still... :)
 .
 .
 .
; later (the actual exec call)
         mov       ax,da                         ; da is the data segment
         mov       ds,ax
         mov       es,ax
         mov       ax,4b00h                      ; call dos
         lea       dx,p_name
         lea       bx,p_block
         int       21h
 .
 .
 .
; and, in the data segment (da)
p_name   db        "M.EXE",0                     ; name of program to run
p_block  label     byte
         dw        0                             ; [1]
         dd        cmdtail                       ; pointer to cmdtail
         dd        fcb1                          ; pointer to fcb1
         dd        fcb2                          ; pointer to fcb2
cmdtail  db        0,0dh                         ; [2]
fcb1     db        0                             ; [3]
         db        11 dup ("?")
         db        25 dup (0)
fcb2     db        0
         db        11 dup (" ")
         db        25 dup (0)
; [1] this is the segment pointer to the environment table to be used by
;     the child program. a value of 0 makes dos produce and use a copy of
;     the running programs psp. you should therefore always use 0 here.
; [2] the command tail is in the format ,"",0dh.
;      does not include the 0dh byte.
; [3] i don't remember if the "?" in fcb1 is necessary. :-/
======
 RH> I have a reference, but I couldn't get it to work.
Then perhaps you need a better reference. :)
 RH> Thanks for any help!
You're welcome. :)
Oh yeah, one last thing. In DOS 2.0, all registers except for CS and IP are
destroyed by function 4B00h. The problem does not exist in DOS 3.0+.
(Let's just pretend you actually needed to know that.. :)
   ("`-/")_.-'"``-._
    O O `; -._   )-;-,_`)
  =(_~_)=  _  )`-.\  ``-'   - Flemming Sondergaard
   _.-~_..-_/ / ((,'
 ((,.-'   ((,/
--- Terminate 4.00/Pro
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